Mechanism of cigarette smoke in promoting small airway remodeling in mice via STAT 3 / PINK 1-Parkin / EMT.

Background: Airway remodeling is an important pathological of airflow limitation in chronic obstructive pulmonary disease (COPD).However,its mechanism still needs to be further clarify.

Methods: Animals:Healthy male C57BL/6 mice aged 4-6 weeks were randomly divided into control group and cigarette smoke(CS)group. Mice in the CS group were placed in a homemade glass fumigator, 5 cigarettes/time, 40 min/time, 4 times/day, 5 days/week, for 24 weeks. Mice in the control group were placed in a normal air environment.Cells:BEAS-2B cells were stimulated with 0.1%cigarette smoke extract(CSE).HE staining, immunohistochemical staining and Masson staining were used to observe the pathological of lung tissues, transmission electron microscopy was used to observe the structural of mitochondria in bronchial epithelial cells.Western blotting was used to detect the expression of STAT3,transforming growth factor-β1(TGF-β1),microtubule-associated protein 1A/1B-light chain3(LC3),PINK1,Parkin,E-cadherin,zonula occludens1(ZO-1),vimentin and snail family transcriptional inhibitor1 (Snail1),and MitoSOX Red was used to detect mitochondrial reactive oxygen species(mtROS).

Results: CS exposure causes lung parenchymal destruction and airway remodeling in mice.Compared to the control group,the expression of p-STAT3,TGF-β1 and EMT in the whole lung homogenate of the CS group was increased.Mitochondrial architecture disruption in bronchial epithelial cells of CS mice, with impaired PINK1-Parkin-dependent mitophagy.In vitro experiments showed that CSE exposure led to STAT3 activation, increased TGF-β1,EMT and enhanced PINK1-Parkin-mediated mitophagy.STAT3 inhibition reversed TGF-β1 upregulation induced by CSE and improved CSE-induced EMT and mitophagy.Inhibition of mitophagy improves EMT induced by CSE. Inhibition of mitophagy reduces STAT3-induced EMT.

Conclusion: CS activates the STAT3,and activated STAT3 promotes EMT in bronchial epithelial cells by enhancing PINK1-Parkin-mediated mitophagy and TGF-β1 signaling.Moreover, activated STAT3 can promote EMT directly.This may be one of the mechanisms by which CS causes small airway remodeling in COPD.